Generally, a sensory signal output apparatus is an apparatus outputting an acoustic or vibration force, such as a speaker, a receiver, a buzzer, and a vibration motor (vibrator) outputting a sound or generating a vibration force by converting an electrical signal inputted from a signal source into a mechanical signal. A bone conduction output apparatus corresponds also to this sensory signal output apparatus.
The sensory signal output apparatus can be applied to various fields according to a size and purpose. In particular, as touch screen phones have become popular, application of a small sensory signal output apparatus, which is widely used for vibration calling for a communication terminal according to the development of information and communication industry, especially, a small vibration motor such as a linear vibration motor having a function beyond a function of the existing rotatory vibration motor, has been rapidly increasing (the conventional vibration motor mainly having a mode that a vibrating screen vibrates while rotating).
The reason why application of the linear vibration motor to portable IT devices, such as touch screen phones including smarts phones, general cellular phones and the like has been extended is because the linear vibration motor has a rapid response speed, a small noise, and a largely improved product life compared with a rotatory vibration motor.
The response speed refers to a time how long it takes the vibration motor to reach 50% of a vibration force at a maximal displacement, and the largest reason for adopting the linear vibration motor is due to the response speed.
As touch screen phones have been recently evolved into smart phones, various applications have been used in the touch screen phones. These applications perform various functions and need feedback vibrations according to the functions. To satisfy the requirement, the development of a vibration motor having a faster response speed than that of the conventional linear vibration motor has been required in the relevant technical field.
The linear vibration motor is distinguished from a vibration motor in which a brush and a commutator are used. The driving principles of the linear vibration motor are based on the Fleming's left-hand law that a conductor that is placed in a magnetic field experience a force in a certain direction. That is, when an AC signal is applied to a fixed coil, the coil generates vibration energy by causing the motion of a magnet, which is a vibrator, according to the direction of an electric current and the size of a frequency.
The conventional linear vibration motor, as illustrated in FIG. 1 of the accompanying drawings, is configured such that a coil 6 is positioned with a distance (gap) in an outward direction or an inward direction of a magnet 4 and a top plate 5 sequentially and fixedly laminated on an upper surface of a yoke 3 using welding, bonding or insertion fixing with the yoke 3 so that a magnet circuit generates a vibration force while vibrating, wherein the magnet circuit reacts to a magnetic flux formed in a gap according to the direction of an alternating signal applied to the coil 6 and includes the magnet 4 and the top plate 5 (the magnet circuit may also include the yoke and/or a weight body depending on a function and design).
In this case, the magnet 3 and the top plate 4 are divided as the magnetic circuit, and the coil 6 is divided as a vibration induced part.
A sensory signal output apparatus having this structure is generally accommodated in a closure type case 1 and cover 2 such that the magnetic circuit including the yoke 6 on which the magnet 4 and the top plate 5 are fixedly seated is supported by a separate leaf spring 7 and is fixed to the case 1 (e.g., rivet 8 fixing, welding fixing, or injection fixing to the case).
However, the conventional sensory signal output apparatus described above is problematic in that a whole volume (size) of the sensory signal output apparatus is increased because the leaf spring 7 supporting the magnetic circuit is disposed in the case 1, and thus a space or a distance for movement of the leaf spring 7 should be secured in the case 1.
In addition, since the conventional sensory signal output apparatus needs work for performing rivet 8 fixing, welding fixing, or injection fixing of the leaf spring 7 to the case 1, manufacturing work is inconvenient and difficult, thereby it is also problematic in that manufacturing properties are reduced.
Also, in the conventional sensory signal output apparatus, since a vibration generated from a vibration structure formed by the coil 6 and the magnetic circuit is transmitted to the case 1 via the leaf spring 7, the vibration force generated from the vibration structure is decreased during a transmission process to a device for which the vibration force is ultimately output, for example, a smart phone, an MP3, a notebook, or the like. Thus, it is problematic in that output efficiency is low.
These problem become more serious in a case, for which a fine vibration force is required, such as a bone conduction output apparatus.
The following documents introduce conventional arts such as the sensory signal output apparatus, and the conventional arts published in this document also have the problems as described above.
Document 1: Korean Patent Laid-Open Publication No. 10-2005-0106482 (Application Number: 10-2005-7016399 (Sep. 2, 2005); Bone Conduction Apparatus)
Document 2: Korean Patent Laid-Open Publication No. 10-2005-0021102 (Application Number: 10-2003-0059198 (Aug. 26, 2003); Diaphragm for Micro Speaker and Micro Speaker Using the Same)